SAT-235 Chronic dexamethasone causes sex- and tissue-specific glucocorticoid resistance in mice

Abstract Disclosure: E.D. Frontera: None. C. Chang: None. J. Meng: None. J.L. Spencer-Segal: None. Background:Glucocorticoid (GC) resistance can occur during prolonged GC excess, but the tissue and sex specificity of this is unknown. We set out to understand the effect of acute versus chronic GC exposure on peripheral and central GC action.Methods: 14-16-week-old male (n=15) and female (n=15) C57Bl6 mice were randomized into 3 groups and received twice daily IP injections for 10 days. The VEH group received 5% ethanol in PBS, the CDEX group 5 mg/kg dexamethasone (DEX) in VEH, and the ADEX group VEH followed by 5 mg/kg of DEX in VEH for the last injection. Tissues were harvested 1 hour after the last injection. Expression of GC-dependent genes Nr3c1, Gilz, Sgk1, Fkbp5, and Mt2a in brain and liver was quantified using RT-qPCR with beta actin used as the control. Data was analyzed in GraphPad Prism using 2-way ANOVA and Tukey’s posthoc tests with ⍺=0.05. Results:In the liver, there was an effect of treatment on Gilz (F(2,20)=3.68 P=0.0437), Sgk1 (F(2,20)=13.58) P=0.002), and Mt2a (F(2,20=5.42 P=0.0132), with the ADEX group having higher levels of these transcripts compared to VEH (P=0.0375 for Gilz, 0.0002 for Sgk1, and 0.0255 for Mt2a). The effect of chronic DEX was transcript-specific. In the CDEX group, Sgk1 was increased compared to vehicle (P=0.0018), but this was not true for Gilz or Mt2a, and Mt2a expression was significantly lower in CDEX relative to ADEX (P=0.0255). There were no sex differences and no effect of treatment on Nr3c1 or Fkbp5. In the brain, there were sex-dependent effects seen as an interaction between sex and treatment on Nr3c1 (F(2,21)=10.95 P=0.0006), Gilz (F(2,21=5.06 P=0.0161), and Fkbp5 (F(2,21)=8.78 P=0.0017). In females, acute DEX increased (P=0.008), and chronic DEX decreased (P=0.0142), Nr3c1 expression, with no treatment effects in males. Chronic DEX also lowered Gilz in females (P=0.0013 relative to VEH, 0.0003 relative to ADEX), with no effect in males. In males, there was a significant induction of Fkbp5 in the ADEX group (P=0.0069) which was lost in the CDEX group (ADEX vs CDEX, P<0.0001). There was a main effect of treatment on Sgk1 (F(2,21=18.09 P=<0.0001) and a significant downregulation of Sgk1 with chronic DEX compared to VEH (P=0.0051) or ADEX (P<0.0001) in both sexes. There was no effect of treatment on Mt2a. Conclusions:We found evidence for sex- and tissue-dependent GC resistance during chronic DEX treatment in mice. Acute DEX more robustly increased GC-dependent gene transcription in liver than in brain, and this increase in liver was lost for Gilz and Mt2a during chronic DEX treatment, indicating a degree of GC resistance. In the brain, chronic DEX tended to downregulate GC-induced genes in a sex-dependent manner, including the receptor itself (Nr3c1) in females. Future work will determine the role of the brain penetrance of DEX in these findings as well as their consequences for the physiological and behavioral effects of systemic GCs. Presentation: Saturday, July 12, 2025